The electronic structure of iron corroles: a combined experimental and quantum chemical study.
There is a longstanding debate in the literature on the electronic structure of chloroiron corroles, especially for those containing the highly electron-withdrawing meso-tris(pentafluorophenyl)corrole (TPFC) ligand. Two alternative electronic structures were proposed for this and the related [FeCl(tdcc)] (TDCC=meso-tris(2,6-dichlorophenyl)corrole) complex, namely a high-valent ferryl species chelated by a trianionic corrolato ligand ([Fe(IV)(Cor)(3-)](+)) or an intermediate-spin (IS) ferric ion that is antiferromagnetically coupled to a dianionic pi-radical corrole ([Fe(III)(Cor)(.2-)](+)) yielding an overall triplet ground state. Two series of corrole-based iron complexes ([Fe(L)(Cor)], in which L=F, Cl, Br, I, and Cor=TPFC, TDCC) have been investigated by a combined experimental (Mössbauer spectroscopy) and computational (DFT) approach in order to differentiate between the two possible electronic-structure descriptions. The experimentally calibrated conclusions were reached by a detailed analysis of the Kohn-Sham solutions, which successfully reproduce the experimental structures and spectroscopic parameters: the electronic structures of [Fe(L)(Cor)] (L=F, Cl, Br, I, Cor=TPFC, TDCC) are best formulated as ([IS-Fe(III)(Cor)(.2-)](+)), similar to chloroiron corrole complexes containing electron-rich corrole ligands. The antiferromagnetic pathway is composed of singly occupied Fe d(z(2) ) and corrole a(2u)-like pi orbitals, with coupling constants that exceed those of analogous porphyrin systems by a factor of 2-3. In the corroles, the combination of lower symmetry, extra negative charge, and smaller cavity size (relative to the porphyrins) leads to exceptionally strong iron-corrole sigma bonds. Hence, the Fe d(x(2)-y(2) )-based molecular orbital is unavailable in the corrole complexes (contrary to the porphyrin case), and the local spin states are S(Fe)=3/2 in the corroles versus S(Fe)=5/2 in the porphyrins. The consequences of this qualitative difference are discussed for spin distributions and magnetic properties.
Ye
Shengfa
S
Lehrstuhl für Theoretische Chemie, Universität Bonn, Wegelerstrasse 12, 53115 Bonn, Germany.
Tuttle
Tell
T
Bill
Eckhard
E
Simkhovich
Liliya
L
Gross
Zeev
Z
Thiel
Walter
W
Neese
Frank
F
D003198:Computer Simulation; D004583:Electrons; D005290:Ferric Compounds / Q000737:chemistry*; D008024:Ligands; D008665:Metalloporphyrins / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D011789:Quantum Theory; D015204:Spectroscopy, Mossbauer; D013237:Stereoisomerism; D013696:Temperature; D005464:Fluorobenzenes; D005466:Fluorocarbons
D005290:Ferric Compounds; D008024:Ligands; D008665:Metalloporphyrins; C442264:tris(pentafluorophenyl)corrole; D005464:Fluorobenzenes; D005466:Fluorocarbons